Method for controlling cam shaft in engine

ABSTRACT

A method for controlling a cam shaft in an engine, may include determining whether a current phase angle of a cam shaft relative to a crank shaft exceeds a predetermined reference range set for determining abnormality of alignment of the cam shaft relative to the crank shaft (S 10 ); when it is determined that the current phase angle exceeds the reference range, determining a control error phase angle which is a difference between the current phase angle and a learned phase angle recently learned as a normal value within the reference range (S 20 ); and controlling an actuator to adjust a phase of the cam shaft and to compensate for an error, taking into account the control error phase angle determined in the determining S 20  (S 30 ).

CROSS REFERENCE TO RELATED APPLICATION

The present application claims priority to Korean Patent Application No. 10-2013-0068115 filed on Jun. 14, 2013, the entire contents of which is incorporated herein for all purposes by this reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a method for controlling a cam shaft in an engine, and more particularly, to a method for controlling the phase of a cam shaft when the phase of the cam shaft relative to a crank shaft is abnormal.

2. Description of Related Art

In a four-stroke cycle-engine, a cam shaft is connected to a crankshaft via a belt, a chain or a gear mechanism, and rotates at a certain ratio relative to the crankshaft so as to open or close the valve at an appropriated time.

In recent years, in order to vary the timing of opening/closing the valve, a continuous variable valve timing (CVVT) system which allows the phase of the cam shaft to be varied relative to the crank shaft is provided. Further, a mechanism is employed which is capable of advancing or delaying the phase of a cam shaft relative to the parts to which the rotational force from a crank shaft is delivered, using an actuator of common hydraulic or electric motor type.

An ECU, which is an engine controller, receives signals from sensors representing operating conditions of the engine such as the number of revolutions of the engine, loads, coolant temperature, oil temperature and altitude, and rotates a cam shaft using an actuator accordingly, such that the timing of opening or closing at least one of an intake valve and an exhaust value is continuously varied according to the conditions of the engine, and ultimately the output of the engine is improved.

In order to optimize engine combustion by such variable valve timing techniques as above, it is essential to accurately control the phase of the cam shaft relative to the crank shaft. Accordingly, the ECU receives the positions of the crank shaft and cam shaft from the respective sensors in real time, and controls the actuator, such that the phase of the cam shaft relative to the crank shaft is controlled accurately and continuously.

However, due to the problems such as bad assembly of an engine or movement of a teeth of timing belt or timing chain to the next position, as shown in FIG. 1 for comparison, if the position of the cam shaft is misaligned relative to the crank shaft 500, then the engine combustion becomes abnormal, and in the worst case catalyst or engine may be possibly damaged due to misfiring.

For your information, the left side of FIG. 1 on one hand shows a normal condition in which both an intake side cam shaft 502 and an exhaust side cam shaft 504 have normal phases relative to a crank shaft 500, and the right side on the other hand shows an abnormal condition in which the intake side cam shaft 502 has misaligned relative to the crank shaft 500.

Conventionally, to cope with such situations, when it is determined that the alignment of the cam shaft relative to the crank shaft exceeds a normal range, variables such as fail determination count or fail determination time are incremented, and when those variables exceed a predetermined threshold value, a corresponding fail code is recorded and Check Engine light is lit on an instrument cluster, and the phase control by the cam shaft is interrupted.

After such a fail determination, the cam shaft is operated while it is fixed to the 0 degree position which is the reference position relative to the actuator. Here, the 0 degree position of the cam shaft is usually set taking into consideration the idle revolution number of an engine, and thus the engine operated at the idle revolution number exhibits the optimal performance at the 0 degree position.

If partial load or full load operation is required in a state that the cam shaft is fixed to the reference position relative to the actuator by the fail determination as described above, then the charging efficient deteriorates due to inappropriate valve opening/closing timings, and the engine fails to generate normal output.

The matters described as the related art have been provided only for assisting in the understanding for the background of the present invention and should not be considered as being acknowledged as a known technology by those skilled in the art.

The information disclosed in this Background of the Invention section is only for enhancement of understanding of the general background of the invention and should not be taken as an acknowledgement or any form of suggestion that this information forms the prior art already known to a person skilled in the art.

BRIEF SUMMARY

Various aspects of the present invention are directed to providing a method for controlling a cam shaft in an engine having a variable valve timing system in a manner that an actuator is controlled so that, even if it is determined that alignment of the cam shaft relative to a crank shaft is abnormal, it allows the engine to operate normally as far as possible, such that malfunction of the engine may be prevented and the operability of the engine may be improved.

In an aspect of the present invention, a method for controlling a cam shaft in an engine, may include determining whether a current phase angle of a cam shaft relative to a crank shaft exceeds a predetermined reference range set for determining abnormality of alignment of the cam shaft relative to the crank shaft (S10), when it is determined that the current phase angle exceeds the reference range, determining a control error phase angle which is a difference between the current phase angle and a learned phase angle recently learned as a normal value within the reference range (S20), and controlling an actuator to adjust a phase of the cam shaft and to compensate for an error, taking into account the control error phase angle determined in the determining S20 (S30).

The method may further include, after the determining S20 and before the controlling of the actuator (S30), when the control error phase angle determined in the determining S20 is greater than a maximum phase angle adjustable by the actuator, setting the control error phase angle to be limited to the maximum phase angle adjustable by the actuator (S25).

In the controlling (S30), the actuator is controlled with a control target phase angle obtained by adding the control error phase angle to a mapping phase angle, which is obtained by adding control correction phase angles according to signals from sensors representing driving conditions of the engine to a control base phase angle, which is a base control value for the phase angle of the cam shaft phase angle.

The method may further include when it is determined that the current phase angle exceeds the reference range as a result of the determining of abnormality (S10), accumulating at least one of count and time of a failure (S15), and determining whether an accumulated failure count exceeds a predetermined threshold value, and when the accumulated failure count exceeds the predetermined threshold value, recording a fail code and lighting up Check Engine light (S40), wherein the controlling of the actuator (S30) is consistently carried out even after the determining of accumulated fail count (S40).

The predetermined threshold value used for comparing the accumulated fail count is set to be a level not influenced by noise which is generated during transition periods in which rapid changes in operating conditions of the engine is made.

The predetermined reference range, which is set for determining whether or not the alignment of the cam shaft relative to the crank shaft is normal, is set to be a smaller range than phase difference which occurs when a teeth of a timing chain connecting the crank shaft and the cam shaft of the engine is moved to the next position.

The methods and apparatuses of the present invention have other features and advantages which will be apparent from or are set forth in more detail in the accompanying drawings, which are incorporated herein, and the following Detailed Description, which together serve to explain certain principles of the present invention.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a diagram for comparing and illustrating a condition in which an intake side cam shaft and an exhaust side cam shaft are normal with a condition in which the exhaust side cam shaft is abnormal, relative to a crank shaft.

FIG. 2 is a flowchart illustrating a method for controlling a cam shaft in an engine according to an exemplary embodiment of the present invention.

FIG. 3 is a diagram conceptually illustrating the operation of the present invention in which a normal condition, a fail condition and a corresponding controlled condition are shown.

It should be understood that the appended drawings are not necessarily to scale, presenting a somewhat simplified representation of various features illustrative of the basic principles of the invention. The specific design features of the present invention as disclosed herein, including, for example, specific dimensions, orientations, locations, and shapes will be determined in part by the particular intended application and use environment.

In the figures, reference numbers refer to the same or equivalent parts of the present invention throughout the several figures of the drawing

DETAILED DESCRIPTION

Reference will now be made in detail to various embodiments of the present invention(s), examples of which are illustrated in the accompanying drawings and described below. While the invention(s) will be described in conjunction with exemplary embodiments, it will be understood that the present description is not intended to limit the invention(s) to those exemplary embodiments. On the contrary, the invention(s) is/are intended to cover not only the exemplary embodiments, but also various alternatives, modifications, equivalents and other embodiments, which may be included within the spirit and scope of the invention as defined by the appended claims.

Referring to FIGS. 2 and 3, a method for controlling a cam shaft in an engine according to an exemplary embodiment of the present invention includes: determining, by a controller, whether a current phase angle ⊖_curr of a cam shaft relative to a crank shaft exceeds a predetermined reference range of ⊖_thrsh_lo to ⊖_thrsh_hi set for determining abnormality of alignment of the cam shaft relative to the crank shaft (S10), if it is determined that the current phase angle exceeds the reference range, calculating, by the controller, a control error phase angle ω_err to be compensated for from a difference between the current phase angle ⊖_curr and a learned phase angle ⊖_earn recently learned as a normal value within the reference range (S20), and controlling, by the controller, an actuator so that it adjusts the phase of the cam shaft so as to compensate for the error, taking into account the control error phase angle calculated in the calculating S20 (S30).

In addition, the method includes: if it is determined that the current phase angle exceeds the reference range as a result of the determining of abnormality S10, accumulating, by the controller, at least one of the count and time of a failure (S15), and determining, by the controller, whether the accumulated failure count C_fail exceeds a predetermined threshold value C_thrsh, and if, so, recording a fail code and lighting Check Engine light (S40). The controlling of the actuator S30 is consistently carried out even after the determining of accumulated fail count S40.

That is, the controller controlling an engine receives a current phase angle of a cam shaft relative to a crank shaft in real time to carry out the determining of abnormality S10, and, depending on the result, controls the actuator taking into account a control error phase angle calculated in the calculating S20. By doing so, abnormality of alignment of the cam shaft is actually detected, and thus the actuator is controlled such that it corrects the control error phase angle not only during but also after failure is ascertained in the determining of accumulated fail count S40 as far as possible. Accordingly, the engine may normally operate and be protected from malfunction or damage.

The method further includes, after the calculating S20 and before the controlling S30, if the control error phase angle ω_err calculated in the calculating S20 is greater than the maximum phase angle ω_max adjustable by the actuator, setting, by the controller, the control error phase angle to be limited to the maximum phase angle adjustable by the actuator (S25).

This is because an error beyond the maximum phase angle adjustable by the actuator cannot be compensated for in any case. The maximum phase angle is determined based on hardware limitations such as whether the actuator is of a hydraulic or electric motor type, or how wide range the actuator has.

In the controlling S30, the actuator is controlled with a control target phase angle ω_target obtained by adding the control error phase angle ω_err to a mapping phase angle ω_map, which is obtained by adding control correction phase angles ω_corr according to signals from the sensors representing the operating environment of an engine to a control base phase angle ω_base, i.e., base control value for the phase angle of the cam shaft.

In existing variable valve timing systems, an actuator is controlled with a mapping phase angle ω_map obtained by adding a control correction phase angle ω_corr to a control base phase angle ω_base, such that control is made based on the default control base phase angle, together with the control correction phase angle reflecting internal and external factors of current engine operating environment. In contrast, in the exemplary embodiments of the present invention, the control error phase angle ω_err obtained as described above is further reflected to determine the control target phase angle ω_target, and control is made according to the control target phase angle ω_target. Accordingly, as can be seen from FIG. 3, if the engine is not operated normally as shown in the left hand but is operated abnormally as shown in the middle, the actuator is controlled according to the control target phase angle as shown in the right hand, so that appropriate timings for opening or closing valves actually necessary for the operating condition of the engine is ensured.

For your information, FIG. 3 symbolically illustrates the operation of the present invention using the conceptual relation between the phase angle of an actuator and the phase angle of a cam shaft connected to the actuator.

The predetermined threshold value C_thrsh used for comparing the accumulated fail count is set to be a level not influenced by noise such that noise generated during the transition periods due to rapid changes in operating conditions of an engine does not affect determination, and thus failure is more accurately determined.

That is, the reference value may be determined when designing based on many experiments so that erroneous determination may be prevented due to electric noise which may be generated during transition periods in which rapid changes in operating conditions of an engine are made, such as start-up of the engine, or sudden acceleration or deceleration.

Further, the predetermined reference range, which is set for determining whether or not the alignment of the cam shaft relative to the crank shaft is normal, may be set to be a smaller range than the phase difference which may occur when a teeth of a timing chain connecting the crank shaft and the cam shaft of the engine is moved to the next position.

In other words, although the current phase angle of the cam shaft relative to the crank shaft may be changed at any time due to various factors such as the assembly tolerance of an engine, output error of a crank shaft or cam shaft sensor, slack of a timing chain or belt, the size of such changes is normally so small that it is distinguishable from the size of the phase angle occurring when at least one teeth of the timing chain is moved to the next position, and, therefore, the reference range may be set within the smaller range than the phase difference in the above situation.

Needless to say, the reference range represents that the current phase angle is not normal, and is determined when designing based on experiments and analyses, which is marked as ⊖_thrsh_lo to ⊖_thrsh_hi in FIG. 2.

By configuring an engine control system operating an actuator according to the method described above, the actuator is controlled so that it consistently corrects errors even when the alignment of a cam shaft is deviated, such that engine may be operated substantially normally and the engine may be protected from malfunction or damage consistently.

The rest of the parts of FIG. 2, which have not been described above, illustrates the followings: if the current phase angle of the cam shaft is determined to be a normal level within the reference range in the determining of abnormality S10, a learned phase angle ⊖_learn is updated with the current phase angle S11, the learned phase angle is stored in a non-volatile memory when the engine is turned off S12, this data is fetched when the engine is started up S13, and this data is used in the calculating S20.

As stated above, according to an exemplary embodiment of the present invention, in an engine having a variable valve timing system, an actuator is controlled so that, even if it is determined that alignment of the cam shaft relative to a crank shaft is abnormal, it allows the engine to operate normally as far as possible, such that malfunction of the engine can be prevented and the operability of the engine can be improved.

The foregoing descriptions of specific exemplary embodiments of the present invention have been presented for purposes of illustration and description. They are not intended to be exhaustive or to limit the invention to the precise forms disclosed, and obviously many modifications and variations are possible in light of the above teachings. The exemplary embodiments were chosen and described in order to explain certain principles of the invention and their practical application, to thereby enable others skilled in the art to make and utilize various exemplary embodiments of the present invention, as well as various alternatives and modifications thereof. It is intended that the scope of the invention be defined by the Claims appended hereto and their equivalents. 

What is claimed is:
 1. A method for controlling a cam shaft in an engine, comprising: determining whether a current phase angle of a cam shaft relative to a crank shaft exceeds a predetermined reference range set for determining abnormality of alignment of the cam shaft relative to the crank shaft (S10); when it is determined that the current phase angle exceeds the reference range, determining a control error phase angle which is a difference between the current phase angle and a learned phase angle recently learned as a normal value within the reference range (S20); and controlling an actuator to adjust a phase of the cam shaft and to compensate for an error, taking into account the control error phase angle determined in the determining S20 (S30).
 2. The method according to claim 1, further comprising, after the determining S20 and before the controlling of the actuator (S30), when the control error phase angle determined in the determining S20 is greater than a maximum phase angle adjustable by the actuator, setting the control error phase angle to be limited to the maximum phase angle adjustable by the actuator (S25).
 3. The method according to claim 2, wherein in the controlling (S30), the actuator is controlled with a control target phase angle obtained by adding the control error phase angle to a mapping phase angle, which is obtained by adding control correction phase angles according to signals from sensors representing driving conditions of the engine to a control base phase angle, which is a base control value for the phase angle of the cam shaft phase angle.
 4. The method according to claim 1, further comprising: when it is determined that the current phase angle exceeds the reference range as a result of the determining of abnormality (S10), accumulating at least one of count and time of a failure (S15); and determining whether an accumulated failure count exceeds a predetermined threshold value, and when the accumulated failure count exceeds the predetermined threshold value, recording a fail code and lighting up Check Engine light (S40), wherein the controlling of the actuator (S30) is consistently carried out even after the determining of accumulated fail count (S40).
 5. The method according to claim 4, wherein the predetermined threshold value used for comparing the accumulated fail count is set to be a level not influenced by noise which is generated during transition periods in which rapid changes in operating conditions of the engine is made.
 6. The method according to claim 1, wherein the predetermined reference range, which is set for determining whether or not the alignment of the cam shaft relative to the crank shaft is normal, is set to be a smaller range than phase difference which occurs when a teeth of a timing chain connecting the crank shaft and the cam shaft of the engine is moved to the next position.
 7. A control system of the engine, comprising the actuator capable of varying a phase angle of the cam shaft relative to the crank shaft, wherein the actuator is controlled according to the method according to of claim
 1. 